Warm up the car and it tells me it is a quart low. So I put in half a quart and let it sit over night and drive it to work the next morning.
When I get to work, it still says that it is a quart low? So I put the rest of the bottle in.

At this point I have drained and added 9 liters total to the engine. Drove to work today and it STILL says I need to add a quart?

Sometimes the computer is slow. After the rod bearing changes I've done it can take quite a while for the computer to decide that it has enough oil in it. Very disconcerting the first time it happened to me after changing the rod bearings on my car. The OP, having the oil draining for an extended time, coupled with the removal of oil from the oil filter housing, may have experienced the same thing. 8 liters might be less than is needed in this situation.

I have driven the car a few times (short distances) and still having the issues. Could the oil level sensor have gone bad? I don't really know what to do at this point. It's still showing I am a quart low.

How much exactly have you driven the car since you changed the oil? If you have put a few hundred miles on it, then I think you are getting an accurate reading and should add oil. If not, then I am not so sure. If you are worried, add a quart, but I would not worry about driving 1 quart low on a 9 quart system unless I was on a racetrack. In the worst case, you can always drain some back out if you get an overfull reading. I have had the overfull reading after being in your situation and continuing to add oil.

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